The growing consensus for an out-of-Africa scenario of modern human dispersal has produced a two-part puzzle of regional variation. Since the last glacial maximum, Europeans developed fairer complexions than any other group on earth, fairer even than others at the same or higher latitudes. Equatorial Native Americans, in contrast, failed to turn very dark over the same time period, despite living at the same latitudes as Africans and Melanesians. This essay suggests a two-part solution. Compared to other high-latitude dwellers, European diet was uniquely cereal-based and so deficient in vitamin D. Compared to other low-latitude dwellers, the ancestors of Native Americans had already lost the alleles necessary for dark brown skin before they crossed Beringia. This essay comprises two parts. Part 1 introduces the puzzle. Part 2 presents the solution.